Awg coupler for separating electromagnetic radiation of various wavelength regions, and a telecommunications system

ABSTRACT

A single free-beam region for coupling electromagnetic radiation in and out is provided in order in the case of an AWG coupler for spectrally separating electromagnetic radiation to achieve a more stable thermal characteristic and a space-saving layout.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an AWG (Arrayed Wave Guide Grating) coupler forspectrally separating electromagnetic radiation that has variousfrequency or wavelength regions.

2. Description of Related Art

Such couplers are used in information processing and telecommunicationsengineering to separate signal-carrying optical bands of electromagneticradiation of different wavelength.

Previous AWG couplers normally have the design illustrated in theleft-hand half of FIG. 2, which takes up a relatively large area. Verysmall bending radii occur in part in the various arms of the previouslyknown coupler, which respectively serve to produce optical path lengthdifferences, as a result of which emission losses and instances ofinfluence on the effective refraction index which impair the performanceproperties of the coupler can occur.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an AWG coupler of thegeneric type that has a smaller spatial extent.

This is achieved in a way that is of most highly surprising simplicitymerely by means of an AWG coupler as disclosed herein.

If this AWG coupler has a 1-to-N transmission region, in particular as afree-beam region for coupling electromagnetic radiation in and out, itis possible by contrast with the prior art to achieve drastic savingswith reference to the space required on the optical substrate.

Moreover, owing to the lower space requirement such a design also hassubstantially improved thermal properties, since a stable temperaturedistribution or constancy of the temperature distribution is easier toachieve in the case of smaller substrates than in the case of theconventional elongated AWG designs.

Furthermore, it is highly advantageous for the conventional coatingtechniques when smaller surface regions are to be coated, since it ispossible thereby to keep the process parameters required and, inparticular, the refractive index differences Δn very much morehomogeneous, as a result of which the properties of the AWG coupler,such as, for example, narrowbandedness or selectivity thereof, can alsobe improved.

Since the substrate area required features quadratically as a rule inthe production costs of the couplers, the inventive AWG coupler has notonly substantially improved performance properties, but can also,moreover, be fabricated more cost-effectively.

If the free-beam region of the AWG coupler is configured such that it ispossible to guide both radiation entering the AWG coupler and radiationexiting from the AWG coupler, it is possible thereby for the guidance ofbeams or waves to the external terminals and into the various arms ofthe coupler to be implemented in a space-saving fashion with the aid ofonly a single optical module, specifically with the aid of the starcoupler that covers the free-beam region.

In a preferred way, the free-beam region covers a star coupler that isdesigned, for example, as a double star coupler such that theelectromagnetic radiation coupled in and that to be coupled out overlap.As a result, it is possible to create particularly space-savingarrangements in the case, in particular, when a plurality of sets ofarms associated with one another are in each case assigned, in a fashionangularly offset in groups in each case, to a group of enteringelectromagnetic radiation and exiting electromagnetic radiation.

If electromagnetic radiation exiting from a first set of arms is fed inthe case of such an arrangement to a second set of arms, it is possibleto achieve substantially steeper filter properties with a singlemultiple AWG coupler arrangement.

In a particularly preferred way, the arms of the AWG coupler, whichdefine the optical path length difference, are coupled to an exitsurface and to an entry surface of one beam coupler, and this permitsnot an elongated design as in the prior art, but a closed design thathas the advantageous reduced dimensions described.

In a particularly preferred way, the AWG coupler has no sharp bends inthe arms which define the optical path length difference, but the armsare arranged on a substantially lobar line, as a result of which it ispossible to reduce substantially emission losses and a worsening of theselectivity of the AWG coupler.

A particularly preferred embodiment of the AWG coupler comprises atwo-dimensional surface wave conductor that is applied to a substrate asa PECVD (Plasma enhanced Chemical Vapor Deposition) layer system and, inparticular, as a PICVD (Plasma induced Chemical Vapor Deposition) layersystem.

Furthermore, the invention permits the advantageous provision ofspatially reduced cost-effective telecommunications systems that areless susceptible to the effect of temperature and have an improvedperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below with the aid ofpreferred embodiments and with reference to the enclosed drawings, inwhich:

FIG. 1 shows the surface layout of an inventive AWG coupler, indicatinghow the latter extends in the surface of an optical substrate,

FIG. 2 shows the comparison between a standard layout and the inventivedesign, it being possible substantially to resolve the same wavelengthdifferences of both systems in conjunction with similar performanceproperties,

FIG. 3 shows the spectral resolution of the conventional and inventiveAWG couplers,

FIG. 4 shows a second inventive embodiment of the AWG coupler, which hasan enlarged free-beam region,

FIG. 5 shows the layout of a third inventive embodiment, in which twoAWG couplers divide a free-beam region,

FIG. 6 shows a layout which is similar to FIG. 5 and in the case ofwhich the input channel of the first AWG coupler crosses the paths ofthe second AWG coupler,

FIG. 7 shows a layout which is similar to FIG. 6 and in the case ofwhich the arms of the two AWG couplers penetrate one another,

FIG. 8 shows a double AWG coupler arrangement in the case of which theelectromagnetic radiation is distributed downstream of the free-beamregion between two asymmetrically arranged AWG couplers, and is coupledout in two output channel groups with substantially half the intensity,and

FIG. 9 shows an AWG coupler provided with incoming and outgoing lines.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of preferred embodiments, reference isfirstly made to FIG. 1, which illustrates the surface layout of aninventive AWG coupler that is denoted overall by the reference numeral1.

This AWG coupler 1 is designed as a two-dimensional waveguidearrangement in the surface of an optical substrate, and is constructedby means of PECVD techniques, in a preferred way by means of PICVDtechniques, as an appropriate layer system with differences inrefractive index, and permits the electromagnetic beams to be guidedreliably in the respective waveguides.

The figures respectively show illustrations which are true to scale forthe purpose of explaining the inventive layout, and have scales that arespecified in the unit of μm.

The AWG coupler 1 from FIG. 1 is a 200 GHz AWG coupler with a centralwavelength of 1.55 μm that is fitted with an input channel 2 and eightoutput channels of which only the output channel marked by the referencenumeral 3 is illustrated by way of example.

The AWG coupler 1 comprises forty arms of which only in each. case everyfifth arm 4 to 12 is illustrated in the figures. The arms 4 to 12respectively produce in steps another optical path length difference,and preferably have a constant optical path length difference in eachcase between two neighboring arms.

The arms 4 to 12 are connected to an exit surface 15 and to an entrysurface 14 of the star coupler 16 such that radiation entering the inputchannel 2 from the star coupler 16 is uniformly projected onto the arms4 to 12 at the exit surface 15.

The electromagnetic radiation moving through the arms 4 to 12 willarrive at the exit surface 14 with a defined transit time difference andafter the effect of a predetermined dispersion defined by the layersystem, and is provided by the star coupler 16, in a fashion that isseparated spectrally or into respective wavelength regions, at eightoutputs thereof.

Of these eight outputs, only the output channel 3 is illustrated by wayof example. However, the person skilled in the art in this field willcertainly know both the design of a star coupler and also the connectionof output channels to the outputs thereof, and this is illustrated inFIG. 9 by way of example.

Reference is made. below to FIG. 2, which illustrates a conventional AWGcoupler, indicated by the reference numeral 17, in its two-dimensionalextent in an exact comparison of size with the inventive AWG coupler 1.

FIG. 3 shows the spectral resolution as a function of wavelength for theconventional and for the inventive AWG coupler 1, and from this theoutstanding selectivity of the latter in conjunction with a lower spacerequirement is yielded unambiguously. In FIG. 3, each first peak isassigned to the conventional AWG coupler, and each second peak isassigned to the inventive AWG coupler 1.

In each case, identical reference numerals are used in the followingdescription of further inventive embodiments for components that areidentical or have an identical effect.

The second inventive embodiment, illustrated in FIG. 4, of the AWGcoupler 1 likewise shows a representation to scale in μm data with anenlarged free-beam region of the star coupler 16. In the case of thisAWG coupler as well as of the AWG coupler 1 of the first inventiveembodiment, and preferably in the case of the star couplers of thefurther inventive embodiments, the arms 4 to 12 lie on virtuallycircular to lobar sections that have clear smaller bending radii thanthe upper region 18 of the conventional AWG coupler. This freebeamregion defines a 1-to-N transmission region within which a transmissionfrom one to N optical paths or from N optical paths to one optical pathis provided. For example, in the embodiments presented here, N has avalue of 36 or 40,standing for 36 or 40 arms.

FIG. 5 illustrates a layout in which two AWG couplers 1, 1′ divide afree-beam region 16 and in which two sets of arms 4 to 12 and 4′ to 12′are in each case assigned, in a fashion angularly offset in groups ineach case, to a group of entering electromagnetic radiation and exitingelectromagnetic radiation.

If, in a further refinement, the two AWG couplers are cascaded in such away that, as illustrated in FIG. 5, the output of the first AWG coupler1 is connected with the aid of an optical conductor 19 to the input ofthe second AWG coupler 1′, it is possible thereby to achieve asubstantially enhanced separation.

FIG. 6 illustrates a layout similar to FIG. 5 in which the entrancechannels 2, 2′ are connected in a space-saving fashion inside the armsof the respective AWG coupler 1, 1′.

FIG. 7 shows a layout in which the arms 4 to 12 and 4′ to 12′ of the twoAWG couplers 1, 1′ penetrate one another in order, once again, to savefurther space and to obtain further advantages of the athermalization.

FIG. 8 shows a double AWG coupler 1, 1′, in which the electromagneticradiation from an input channel 2 is distributed downstream of thefree-beam region 16 with substantially the same intensity between twoasymmetrically arranged AWG couplers 1, 1′, and is coupled out withessentially half the intensity in each case in two output channel groups3, 3′. This yields a beam divider function that advantageously providestwo output channels 3, 3′ with spectrally separated signals given onlyone input channel 2.

FIG. 9 shows an illustration of the principle of an inventive AWGcoupler 1 that is provided with one incoming line 19 at its inputchannel 2 and outgoing lines 20 to 27 at its output channel 3.

1. An AWG coupler for spectrally separating electromagnetic radiation,comprising: a 1-to-N transmission region for coupling in and couplingout electromagnetic radiation, and a plurality of arms that define anoptical path length difference, the plurality of arms being coupled toan exit surface and an entry surface so that the plurality of arms lieon a lobar line, wherein the AWG coupler is a two-dimensional surfacewave conductor applied to a substrate as a PECVD layer system.
 2. TheAWG coupler as claimed in claim 1, wherein the 1-to-N transmissionregion is a free-beam region that can guide both electromagneticradiation entering the AWG coupler and electromagnetic radiation exitingfrom the AWG coupler.
 3. The AWG coupler as claimed in claim 2, whereinthe free-beam region defines a star coupler.
 4. The AWG coupler asclaimed in claim 3, wherein the star coupler is a double star coupler sothat the electromagnetic radiation coupled in and coupled out overlap.5. The AWG coupler as claimed in claim 1, wherein the plurality of armsare angularly offset to a group of entering electromagnetic radiationand exiting electromagnetic radiation.
 6. The AWG coupler as claimed inclaim 5, wherein electromagnetic radiation exiting from a first set ofarms is fed to a second set of arms.
 7. A telecommunications systemcomprising: an AWG coupler having a plurality of arms that define anoptical path length difference, the plurality of arms being coupled toan exit surface and an entry surface so that the plurality of arms lieon a lobar line, wherein the AWG coupler is a two-dimensional surfacewave conductor applied to a substrate as a PECVD layer system.
 8. Thetelecommunications system as claimed in claim 7, wherein the 1-to-Ntransmission region is a free-beam region that can guide bothelectromagnetic radiation entering the AWG coupler and electromagneticradiation exiting from the AWG coupler.
 9. The telecommunications systemas claimed in claim 8, wherein the free-beam region defines a starcoupler.
 10. The telecommunications system as claimed in claim 9,wherein the star coupler is a double star coupler so that theelectromagnetic radiation coupled in and coupled out overlap.
 11. Thetelecommunications system as claimed in claim 7, wherein the pluralityof arms are angularly offset to a group of entering electromagneticradiation and exiting electromagnetic radiation.
 12. Thetelecommunications system as claimed in claim 11, whereinelectromagnetic radiation exiting from a first set of arms is fed to asecond set of arms.